Rectification. A few time ago I answered to the question how to visualise the effect of the tilt of the earth axis to the equation of time.
I suggested to draw an equatorial coordinate system and an ecliptical coordinate system in one drawing. I wrote : "Draw a circle with radius R. Draw a vertical and horizontal diameter. The vertical diameter intersects the circle in the poles, the horizontal diameter is the equator. On the equator draw points at distance R.sin30 and R.sin60 from the center. (0.5R and 0.866R) Do this at both sides of the center. Draw 4 arcs through the 2 poles and the just constructed points. Now you have a part of the equatorial coordinate system. Draw in this figure ( with other color if you like ) in the same way a second coordinate system, but with the 2 diameters rotated over 23.5 degrees to the left ( or right if you like it that way). This is the ecliptical coordinate system." This will do to visualise the given problem, but the construction isn't correct. Instead of drawing arcs through the poles ellipses have to be drawn. In that case the coordinate system is as in the astrolabe of Roias and that is what I meant to answer. Sorry for my error. Fer J. de Vries.
